Currently meta viewport tag support is enabled at runtime on Android, but disabled on all other platforms, even touchscreens like Chromebook Pixel and Windows 8.
I spoke to Rick about this a while ago, and he said for compatibility reasons he'd rather never support the meta viewport tag on desktop, but that it would make sense to support CSS Device Adaption (@viewport) uniformly across all platforms (see also issue 155477).
The main difference being, that many sites written for meta viewport tag might assume the tag will only be applied on mobile, whereas sites using @viewport are more likely to take into account touchscreen laptops, and realise that they have to test @viewport on desktop too.
This sounds reasonable. This meta-bug tracks anything that blocks enabling @viewport on platforms other than Android.

FWIW I'm now leaning towards trying to support the whole viewport meta tag on ChromeOS - see issue 232102 . We just need to see how many sites are broken by this (under the assumption that it's mobile-specific).
Regardless, I agree that enabling @viewport should be done for all platforms at essentially the same time. We shouldn't propagate the mobile/desktop divide for new web platform features...

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I was wondering what we should do with this? We've had the @viewport code behind a flag (and quite well-tested) for years now, but there's not any momentum towards launching it because in practice, we haven't seen compelling use cases. (The dominant use of meta viewport is just "width=device-width" which is equivalent to desktop browsers' behavior anyway.)
Is it time to start thinking about deleting the implementation from Blink instead?

The discussion has been recently resurrected in https://github.com/w3c/csswg-drafts/issues/258
My read is that the current design of @viewport will never be shipped but there may be some redesign to make it less of a performance footgun. It would be nice to have something to be able to set pinch-zoom limits on desktop so I'd like to see something here ship but I don't think we should keep it around indefinitely if this fails to move forward again. Perhaps Yoav's suggestion of just adding an attribute to the viewport <meta> to make it apply on desktop is enough?